1. Field of the Invention
The present invention relates to a plate-like or sheet-like element for filtering a fluid flowing therethrough. Filter elements of this type may, for example, by used as a venting filter for stoma bags, which means collection pouches for receiving drainage from an abdominal opening following surgery. The filter element of the type in question may also be used in gas masks, as air inlet filter in combustion engines, and for several other purposes, where a liquid or gaseous fluid is to be filtered in order to remove solid particles and/or certain gaseous or liquid components therefrom.
2. Description of Prior Art
A filter element of the above type for use as a venting filter for stoma bags is disclosed in U.S. Pat. No. 3,759,260. This known filter element comprises a filter disc of matted fibers and granular activated carbon, and the filter disk is covered by and sandwiched between a pair of plastic sheets, which are sealed at the periphery of the disk. A central gas outlet opening is provided in one of the plastic sheets, and gas inlet openings are provided along the periphery of the disk. In this known filter element, the plastic sheets loosely engage with, but do not adhere to, the opposite side surfaces of the filter. German patent No. 613,113 discloses a filter element of the same type, where the plastic sheets adhere to the adjacent side surfaces of the filter disk by means of an adhesive, and the oppositely arranged plastic sheets are separated along the periphery of the filter element so that the filter disk, which is made from matted fibres and activated carbon enclosed therein, is exposed along the periphery thereof.
In the former known filter element, the gas flowing from the interior of an associated stoma bag tends to flow through passages defined between the filter disk and the adjacent plastic sheet, whereby the gas does not come into the intended intimate contact with the granulated carbon contained in the filter disc. In the latter known filter element, where the plastic sheets are glued to the adjacent opposite surfaces of the filter disk, the gases to be filtered are forced to flow through the mattet fibres, when passing radially through the filter.
However, the filtering or absorption capacity of a gas filter of the above type is to a high extent dependent on the amount of active substance, such as activated carbon, which is contained in each volume unit of the filter material sandwiched between the gas impervious cover sheets or plastic sheets, and, consequently, the minimum dimensions of a filter element of the type in question are dependent on the content of the active substance. The active substance, such as activated carbon, is embedded in a matrix formed by matted fibers. Normally, a high content of the activated carbon causes a reduction of the cohesion of the fibrous material, and in some cases the fibrous material even tends to delaminate. Therefore, even when the covering plastic sheets are glued to the adjacent surfaces of the filter disk, undesired flow passages may be formed in the fibrous material, whereby the gas flow through the filter element is not uniformly distributed, so that the efficiency of the filter is reduced. Furthermore, a high content of activated carbon or another active substance within the fibrous filter disk will normally make the gluening of the covering plastic sheets to the fibrous filter disk more difficult.